AZ L-85 Wastewater Treatment Contractor
Exam Questions and Correct Answers (Verified
Answers) Plus Rationale 2027 Q&A| Instant
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1. What is the primary purpose of preliminary treatment at a
wastewater treatment facility?
a. Remove dissolved nutrients
b. Disinfect the final effluent
c. Remove large debris, grit, and other materials that could damage
downstream equipment
d. Increase the biological oxygen demand of the wastewater
Rationale: Preliminary treatment protects pumps, pipes, screens, and
other equipment by removing large objects, rags, grit, and similar
materials before the wastewater enters subsequent treatment
processes.
, 2. Which device is commonly used to remove large floating debris
from incoming wastewater?
a. Trickling filter
b. Clarifier
c. Bar screen
d. Chlorine contact tank
Rationale: Bar screens consist of parallel bars that intercept large solids
such as rags, sticks, plastics, and other debris. Removing these materials
prevents clogging and equipment damage.
3. What is grit primarily composed of?
a. Dissolved organic matter
b. Sand, gravel, and other dense inorganic particles
c. Bacteria and viruses
d. Dissolved nitrogen compounds
Rationale: Grit is primarily inorganic material that settles rapidly
because of its relatively high density. Removing it helps prevent
abrasion, sediment accumulation, and reduced capacity in downstream
units.
4. What is the primary function of a primary clarifier?
,a. Add oxygen to wastewater
b. Disinfect wastewater
c. Settle suspended solids and remove floating scum
d. Convert ammonia directly into nitrogen gas
Rationale: Primary clarifiers provide relatively quiescent conditions that
allow heavier suspended solids to settle while lighter materials such as
grease and scum rise to the surface for removal.
5. Which measurement is commonly used to indicate the amount of
oxygen required to biologically oxidize biodegradable organic
matter?
a. TSS
b. pH
c. BOD
d. DO
Rationale: Biochemical oxygen demand (BOD) estimates the oxygen
microorganisms require to biologically stabilize biodegradable organic
material in wastewater.
6. What does TSS stand for?
a. Total Soluble Salinity
b. Treatment System Standard
, c. Total Suspended Solids
d. Total Sediment Stabilization
Rationale: Total suspended solids are particles suspended in water that
can be retained by an appropriate filtration method. TSS is an important
indicator of treatment performance and effluent quality.
7. Why is dissolved oxygen important in an aerobic biological
treatment process?
a. It prevents all solids from settling
b. It increases wastewater temperature
c. It provides oxygen needed by aerobic microorganisms
d. It eliminates the need for clarification
Rationale: Aerobic microorganisms require dissolved oxygen to
metabolize organic matter. Maintaining adequate DO supports
biological treatment and helps prevent undesirable anaerobic
conditions.
8. What is the purpose of an aeration basin in an activated-sludge
process?
a. Remove only large debris
b. Store treated drinking water
Exam Questions and Correct Answers (Verified
Answers) Plus Rationale 2027 Q&A| Instant
Download Pdf
1. What is the primary purpose of preliminary treatment at a
wastewater treatment facility?
a. Remove dissolved nutrients
b. Disinfect the final effluent
c. Remove large debris, grit, and other materials that could damage
downstream equipment
d. Increase the biological oxygen demand of the wastewater
Rationale: Preliminary treatment protects pumps, pipes, screens, and
other equipment by removing large objects, rags, grit, and similar
materials before the wastewater enters subsequent treatment
processes.
, 2. Which device is commonly used to remove large floating debris
from incoming wastewater?
a. Trickling filter
b. Clarifier
c. Bar screen
d. Chlorine contact tank
Rationale: Bar screens consist of parallel bars that intercept large solids
such as rags, sticks, plastics, and other debris. Removing these materials
prevents clogging and equipment damage.
3. What is grit primarily composed of?
a. Dissolved organic matter
b. Sand, gravel, and other dense inorganic particles
c. Bacteria and viruses
d. Dissolved nitrogen compounds
Rationale: Grit is primarily inorganic material that settles rapidly
because of its relatively high density. Removing it helps prevent
abrasion, sediment accumulation, and reduced capacity in downstream
units.
4. What is the primary function of a primary clarifier?
,a. Add oxygen to wastewater
b. Disinfect wastewater
c. Settle suspended solids and remove floating scum
d. Convert ammonia directly into nitrogen gas
Rationale: Primary clarifiers provide relatively quiescent conditions that
allow heavier suspended solids to settle while lighter materials such as
grease and scum rise to the surface for removal.
5. Which measurement is commonly used to indicate the amount of
oxygen required to biologically oxidize biodegradable organic
matter?
a. TSS
b. pH
c. BOD
d. DO
Rationale: Biochemical oxygen demand (BOD) estimates the oxygen
microorganisms require to biologically stabilize biodegradable organic
material in wastewater.
6. What does TSS stand for?
a. Total Soluble Salinity
b. Treatment System Standard
, c. Total Suspended Solids
d. Total Sediment Stabilization
Rationale: Total suspended solids are particles suspended in water that
can be retained by an appropriate filtration method. TSS is an important
indicator of treatment performance and effluent quality.
7. Why is dissolved oxygen important in an aerobic biological
treatment process?
a. It prevents all solids from settling
b. It increases wastewater temperature
c. It provides oxygen needed by aerobic microorganisms
d. It eliminates the need for clarification
Rationale: Aerobic microorganisms require dissolved oxygen to
metabolize organic matter. Maintaining adequate DO supports
biological treatment and helps prevent undesirable anaerobic
conditions.
8. What is the purpose of an aeration basin in an activated-sludge
process?
a. Remove only large debris
b. Store treated drinking water
